Phthalocyanine, naphthobenzoporphyrazine and porphyrin derivatives (Pc's) are blue-green dyes which are photosensitive. These dyes are known as useful for a variety of industrial or bio-medical applications. For example, as photosensitizing agents, these compounds are particularly attractive for in vivo treatment of cancer and the in vitro photoinactivation of viruses in blood products. The effective photoinactivation of Streptococcus faccium and Candida albicans through damage at the membrane level, mediated by Pc's also suggests their usefulness in sterilization processes. In addition to medical applications, Pc's and their analogues can be useful as photocatalysts (chemically modified electrodes) for energy conversion processes. Another known application is found in the preparation of thin films useful for detecting volatile compounds even at very low concentrations. In this regard, the behaviour of monosulphonated Pc's featuring hydrophobic electron-withdrawing (F.sup.-) or electron-donating (t-Bu) substituents in the benzo rings, as in provided by the process of the present invention, are of major interest.
However, one of the most promising application of Pc's remains the photodynamic therapy (PDT) of cancer tumours. PDT is based on the use of a photosensitizing dye, such as Pc's which, upon localization at the tumour site and light activation in the presence of oxygen, produces cytotoxic species, including singlet oxygen, resulting in tumour necrosis.
The amphiphilic nature of Pc derivatives obtained in accordance with the process of the present invention allows them to easily interact with cells membranes which renders the derivatives particularly attractive photosensitizing agents for in vivo photodynamic therapy of cancer. Pc's tend to localize in tumours as opposed to healthy tissues such as muscles, skin, heart and lungs. The larger openings (500-1000 .ANG. in diameter) of tumour capillaries and the larger interstitial area of tumour cells renders tumours more permeable to Pc's than other parts of the body. Hence the Pc's accumulate in tumours. Their capacity to photo-inactivate cancer cells in vitro as well as in vivo is well documented and particularly mono/disulphonated, amphiphilic phthalocyanines, chelated with diamagnetic metal ions have been shown capable of inflicting direct tumour cell kill.
One of the major stumbling blocks in the preparation and use of Pc's has been their synthesis methods which has generally complicated, long and result in complex mixtures of compounds requiring difficult purification steps.
Known synthesis routes for the preparation of amphiphilic phthalocyanines mainly consist of one of following two methods:
(i) in situ synthesis of the phthalocyanines macrocycle, i.e. condensation of two differently substituted precursors in the appropriate stoichiometric ratio and PA0 (ii) partial sulphonation of substituted metallo phthalocyanines.
These methods can be inconvenient for several reasons. Thus, in the first known method, the syntheses of amphiphilic phthalocyanine via the mixed condensation method requires two types of precursors (hydrophillic and lipophilic), which differ substantially in their physical properties and reactivities, disfavouring selection of optimal reaction conditions and stoichiometry. Furthermore, the complexity of the resulting reaction mixture requires time consuming and tedious chromatographic separation procedures.
The second known method results in even more complex isomeric mixtures due to sulphonation either at 3- and 4-positions of the benzo rings of the phthalocyanine macrocycle. Also, electrophilic substitution requires harsh reaction conditions which may affect substituents, result in demetallation or decomposition of the macrocycle.
Accordingly, there is a great need for an improved process for preparing substantially pure, single positional isomers of phthalocyanines and analogous compounds such as naphtophthalocyanines and porphyrins.
A known method developed by Meerwein and co-workers, useful for converting aromatic amines to sulphonyl chlorides, involves treatment of the diazonium chloride in concentrated hydrochloric acid with sulphur dioxide in acetic acid, using the cupric ion as a catalyst (E. E. Gilbert, Sulphonation and Related Reactions, Interscience Publishers, New York, 1965, p. 171). However, the method was not thought to be applicable for the synthesis of Pc's due to the low solubility of the monodiazonium salts of phthalocyanines, naphthobenzoporphyrazines and tetraphenylporphyrins in water (or aqueous acetone).
In the present invention, it was surprisingly found that the Meerwein procedure could be ingeniously modified to accommodate the specific properties of the selected macrocyclic compounds. In accordance with the present invention, suspensions or solutions of monodiazo compounds were used and the completion of the reaction was established empirically. To optimize the use of the monodiazo compounds, the order by which reagents were added was reversed.